Method for determining at least one geometrico-morphological parameters of a subject in a natural posture for determining a vision correction equipment

ABSTRACT

Disclosed is a method wherein the following steps are performed: a) the subject is placed in a natural posture, in which at least one of the gaze directions of the subject points to a visual target, b) an image capture apparatus is placed between the head of the subject and the visual target, c) the relative posture of the image capture apparatus and head of the subject is adjusted in order for the pupil of the image capture apparatus to be positioned close to the gaze direction of at least one of the eyes of the subject, d) an image of the head of the subject is captured, and e) the at least one geometrico-morphological parameter is deduced from this image.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for determining at least onegeometrico-morphological parameter of a subject in a natural posture fordetermining a vision correction equipment.

BACKGROUND INFORMATION AND PRIOR ART

Manufacturing an ophthalmic lens adapted to an individual and a frame inorder to provide the individual with appropriate ophthalmic equipmentrequires the determination of a number of fitting data for fitting thelens in the chosen frame.

In order to obtain these fitting data, the determination ofgeometrico-morphological parameters of the subject is necessary.

Numerous documents describe devices and methods for determining suchparameters. These parameters are for example the interpupillary distanceof the subject or the fitting height, defined as the vertical distancebetween the pupil of the eye of the subject and the bottom edge of theframe or lens worn by the subject, in use conditions.

In order to be accurate, the measurement of the geometrico-morphologicalparameters of the subject such as the fitting height requires thesubject to be in a natural posture.

However, it is always difficult to ensure that the subject remains inthe natural posture during the image capture that will allow thedetermination of these parameters.

Therefore, the repeatability of known methods is not alwayssatisfactory.

Moreover, known methods often require the use of specific instrumentsthat are not easily available to the general public.

Finally, known methods usually require the intervention of an eye careprofessional. For example, the eye care professional may manuallymeasure the fitting height with a ruler.

For these reasons, known methods do not allow precisely determining thegeometrico-morphological parameters of the subject in a natural posture.

Moreover, they do not allow self determination of the parameter by thesubject himself.

SUMMARY OF THE INVENTION

Therefore one object of the invention is to provide a simple method fordetermining at least one geometrico-morphological parameter in areliable natural posture.

The above object is achieved according to the invention by providing amethod for determining at least one geometrico-morphological parametersof a subject in a natural posture for determining a vision correctionequipment, wherein the following steps are performed:

a) the subject is placed in a natural posture, in which at least one ofthe gaze directions of the subject points to a visual target,

b) an image capture apparatus is placed between the head of the subjectand said visual target,

c) the relative posture of the image capture apparatus and head of thesubject is adjusted in order for the pupil of the image captureapparatus to be positioned close to the gaze direction of at least oneof the eyes of the subject,

d) an image of the head of the subject is captured,

e) the at least one geometrico-morphological parameter is deduced fromthis image.

Thanks to the position adjustment of step c), the eyes of the subjectremains focused on the visual target. Therefore, they do not focus onthe pupil of the camera. It is therefore easier for the subject toremain in the posture corresponding to a far, intermediate or neardistance vision, with an eye gaze directed straight ahead of thesubject, to the visual target. The posture adopted by the subject instep a) is therefore unchanged by the placement of the image captureapparatus in front of the subject. The visual target may correspond to afar distance, intermediate distance or near distance visual task.

Instructions given to the subject are simple and easy to follow, leadingto a better repeatability of the method.

A further object of the invention is to provide a method that thesubject is able to perform by himself. The subject is then able toperform said method by himself, with an electronic device of his own. Inthis way, the subject may determine the geometrico-morphologicalparameter by himself, at home or in any other location remote from theeye care professional's office.

Alternatively, the method according to the invention may also beimplemented with dedicated tools and optional help from the eye careprofessional.

Advantageous and non-limiting features of the method of the inventionare:

-   -   in steps c) and d), the gaze direction of at least one of the        eyes of the subject points to said visual target;    -   in step c), the relative posture of the image capture apparatus        and head of the subject is adjusted by moving the image capture        apparatus without moving the head of the subject, in step d),        the gaze direction of both eyes of the subject points to said        pupil of the image capture apparatus and, in step e), the        distance between the image capture apparatus and the eyes of the        subject is taken into account for determining said parameter;

in step b), the image capture apparatus belongs to a personal electronicportable device of the subject;

in step b), the subject presses the image capture apparatus against theglass of the window and, in step c), the subject moves the image captureapparatus against the glass of the window;

the steps a) to c) are performed by the subject himself: in step a), thesubject places himself in the natural posture and, in step b) and c),the image capture apparatus is manually held and moved by the subject;

the image capture apparatus comprises an inertial motion unit adapted todetermine the angular position in space of the image capture apparatus,and a communication device adapted to send information on the angularposition in space of the apparatus to the subject and, in step c), theimage capture apparatus provides information to the subject on theangular position of the apparatus compared to a target angular position;

in step d), the image capture is triggered by the subject orautomatically triggered by the image capture apparatus when the head ofthe subject is detected by said image capture apparatus;

the image capture apparatus is attached on a column and verticallymobile on this column;

in step e), at least one of the following parameters is determined:interpupillary distance, half interpupillary distance, fitting heights;

in step e) the dominant eye of the subject is also determined;

the image capture apparatus is positioned such that the image captureapparatus optical axis is close or parallel to the gaze direction of thesubject during the capture of said image of the head of the subject;

a reference element for scaling the image is placed close to the head ofthe subject and, in step d), an image of the reference element iscaptured with the image of the head of the subject; and

in step d), the subject wears no real frame and a three dimensionalimage of the head of the subject is captured by said image captureapparatus, in step e), a virtual frame is virtually fitted on the threedimensional image of the head of the subject and a two dimensional imageof the head of the subject wearing said virtual frame is deduced, andthe fitting height parameter is determined on the basis of this twodimensional image.

Preferably, in step c), the inclination of the image capture apparatusis adjusted in order for the head of the subject to be in the field ofthe image capture apparatus.

In an embodiment, in step d), the subject wears the chosen frame.

In another embodiment, in step e), an error of parallax is taken intoaccount for determining said parameter.

In an embodiment, in step c), the image capture apparatus is moved bythe subject or another person, either directly or indirectly.

The invention also relates to a system for determining at least onegeometrico-morphological parameters of a subject in a natural posturefor determining a vision correction equipment, comprising:

a visual target adapted to be placed in front of the subject, such thatthe subject is placed in a natural posture when at least one gazedirection of the subject points to said visual target,

an image capture apparatus adapted to be placed between the head of thesubject and said visual target and to capture an image of the head ofthe subject,

adjusting means for adjusting the position and/or orientation of theimage capture apparatus in order for the pupil of the image captureapparatus to be positioned close to the gaze direction of at least oneof the eyes of the subject,

calculating means programmed for deducing the at least onegeometrico-morphological parameter from said image of the head of thesubject captured with said image capture apparatus.

DETAILED DESCRIPTION OF EXAMPLE(S)

The following description, enriched with joint drawings that should betaken as non limitative examples, will help understand the invention andfigure out how it can be realized.

On joint drawings:

FIG. 1 is a block diagram of the steps of an embodiment of the methodaccording to the invention,

FIG. 2 is a schematic side view of a first possible relative position ofthe subject, electronic device and target during step d),

FIG. 3 is a schematic side view of a second possible relative positionof the subject, electronic device and target during step d),

FIG. 4 is a schematic view from above of the first possible relativeposition of the subject, electronic device and target during step d).

In the following, the wording “natural posture” is defined as a posturein which the position of the head is not imposed by a physicalconstraint such as applying a part of the head against a surface.

According to the invention, the method for determining at least onegeometrico-morphological parameters of a subject in a natural posturefor determining a vision correction equipment comprises the followingsteps:

a) the subject is placed in a natural posture in which at least one ofthe gaze directions of the subject points to a visual target 20 (block100 of FIG. 1),

b) an image capture apparatus 10 is placed in front of the head 50 ofthe subject (block 200 of FIG. 1),

c) the relative posture of the image capture apparatus 10 and head 50 ofthe subject is adjusted in order for the pupil P of the image captureapparatus 10 to be positioned close to the gaze direction GDL, GDR of atleast one of the eyes OL, OR of the subject (block 300 of FIG. 1),

d) an image of the head 50 of the subject is captured (block 400 of FIG.1),

e) the at least one geometrico-morphological parameter is deduced fromthis image (block 500 of FIG. 1).

In a first embodiment of the method according to the invention, theimage capture apparatus 12 belongs to a portable electronic device 10that the subject holds is his own hands.

The portable electronic device 10 is for example a smartphone or adigital tablet. It is for example a personal device of the subject. Itcomprises a body 11 with a screen and the image capture apparatus 12.

Instructions for performing the method may be provided to the subjectvia the portable electronic device. For example, the instructions maybedisplayed on a screen of this device when the subject runs anapplication dedicated to implementing the method according to theinvention.

In this case, the front camera of the smartphone, placed beside thescreen is advantageously used so that the subject may read theinstructions and capture the image without having to turn thesmartphone.

Alternatively, it may be a portable electronic device equipped with asupport allowing it to be placed in front of the head of the subject.The support is for example a stand adapted to be moved and with anadjustable height.

In a second embodiment (not shown on the figures), the image captureapparatus is attached on a column and vertically mobile. It is forexample a camera or a smartphone.

In this case, instructions for performing the method may be provided tothe subject via a screen placed on the column or given orally by anoperator assisting the subject in performing the method.

Step a)

In step a), represented as block 100 on FIG. 1, the subject is placed ina natural posture.

Preferably, the subject places himself in the natural posture.

To this end, instructions are given to the subject to gaze at a visualtarget 20 placed at a specified distance D1 from his eyes (FIGS. 2 to4).

At least one of the gaze directions GDL, GDR of the subject points tosaid visual target 20. Preferably, in step a), both of his gazedirections GDR, GDL points to the visual target 20.

The gaze direction GDR, GDL of each eye OR, OL of the subject is definedas the line linking the pupil of said eye to the point on which the eyeis focused (FIG. 4). This gaze direction also corresponds to the linepassing through the eye rotation center and the pupil center.

For example, if the geometrico-morphological parameter is to bedetermined in conditions of far vision, it is indicated to the subjectthat he should gaze at a target 20 placed as far as possible from him.This target 20 may be for example the horizon or a building placed farahead or any target placed at a distance D1 of more than five meters.This case is shown on FIGS. 2 to 4. The figures are schematic and not toscale.

In this case, the natural posture assumed by the subject is preferablythe posture where he looks straight ahead to the horizon without anyconstraint. This natural posture is also called orthostatic posture andcorresponds to the position in which the individual achieves minimalefforts. The corresponding gaze directions are the primary gazedirections.

In this natural posture, the Frankfurt plane of the head is horizontal.The Frankfurt plane is defined as the plane passing through the inferiormargin of an orbit (for example, the point called the left orbital) andthe upper margin of each ear canal or external auditory meatus, a pointcalled the porion.

In a particularly advantageous embodiment, the subject may place himselfin front of a window 30 and gaze straight ahead at a distant targetthrough the window 30. The gaze direction GDR, GDL of the subject isthen the primary gaze direction and the posture of the subject is theorthostatic posture.

If the geometrico-morphological parameter is to be determined inconditions of intermediate vision, it is indicated to the subject thathe should gaze at a target placed at a distance of about one meter, forexample comprised between 80 centimeters and 5 meters. This target maybe for example a frame on a wall or a computer screen. In this case thesituation is similar to the situation shown on FIGS. 2 to 4.

If the geometrico-morphological parameter is to be determined inconditions of near vision, it is indicated to the subject that he shouldgaze at a target placed at a reading distance from him, for examplebetween 25 and 50 centimeters. This target may for example comprise atext or a book placed in one of his hands or on a support, for example atable. In this case, the subject's gaze may be inclined toward thetarget, with a non zero angle relative to the horizontal direction. Inthis case, the natural posture is preferably the posture naturallyassumed by the subject when reading a text (not represented on thefigures).

Step b)

In step b), said image capture apparatus 12 is placed in front of thehead 50 of the subject.

This image capture apparatus 12 may capture images in two or threedimensions. It may be for example the front or back camera of asmartphone or tablet, or means for acquiring three dimensional data,such as images using infra-red camera and infra-red spots projected onthe head of the subject used to identify the face of the user of thesmartphone.

The image capture apparatus 12 is placed between the head 50 of thesubject and said visual target 20 as shown on FIGS. 2 to 4. This isverified for any distances between the head 50 and the visual target 20.

The image capture apparatus 20 may be placed in front of the head of thesubject by the subject or another person.

In the first embodiment, the portable electronic device comprising theimage capture apparatus is preferably placed in front of the subject byhimself.

In said particularly advantageous embodiment, the subject may place theelectronic portable device in front of his head 50 by placing it againstsaid window 30. He presses the electronic portable device 10 with theimage capture apparatus 12 against the glass of the window 30. Forexample, the subject holds the image capture apparatus at arm's length.

He is then instructed to visually superimpose the pupil P of the imagecapture apparatus 12 with the target 20 at step c).

In the second embodiment, the column is placed in front of the subjecteither by himself, by placing himself in front of the column or byanother person, for example an operator assisting him by leading him tothe column.

The subject may be seated or standing in front of the image captureapparatus 12.

Step c)

In step c), the relative posture of the image capture apparatus 12 andhead 50 of the subject is adjusted in order for the pupil P of the imagecapture apparatus 12 to be positioned close to the gaze direction GDL,GDR of at least one of the eyes OL, OR of the subject.

The image capture apparatus is positioned close to the gaze direction ofat least one of the eyes of the subject. Preferably, the pupil P of theimage capture apparatus 12 is placed on the gaze direction GDR of one ofsaid eyes OL, OR (FIGS. 2, 4).

Otherwise, it is preferably placed in a solid angle of about 1 to 10degrees around the gaze direction of said at least one eye (FIG. 3).

FIG. 3 show an example where the pupil of the image capture apparatus isshifted relative to both of the gaze direction of the subject.

It is for example shifted towards the floor.

In order to perform this adjustment, the head 50 of the subject and/orthe image capture apparatus 12 may be moved relative to each other.

The image capture apparatus may be moved by the subject or anotherperson, either directly or indirectly.

The subject may move his head and/or the image capture apparatus 12 byhimself.

In the first embodiment, the portable electronic device 10 is preferablymoved directly by the subject who holds it in his hand. The relativeposture of the image capture apparatus 12 and head 50 of the subject isadjusted by moving the image capture apparatus 12 without moving thehead 50 of the subject.

In the particularly advantageous embodiment described before, thesubject moves the electronic portable device 10 with the image captureapparatus 12 against the glass of the window 30. More precisely, hemoves the electronic portable device 10 by translating it against thewindow. His head 50 remains in same position.

The subject is for example asked to move the image capture apparatus,that is to say, here, the smartphone, until the pupil P of the imagecapture apparatus 12 is placed right in front of one of his eyes OL, OR.The pupil P of the image capture apparatus 12 is then visuallysuperimposed with the target 20.

Advantageously, in this situation the head of the subject will usuallybe entirely in the field of the image capture apparatus.

In the second embodiment, the subject may move his head 50 relative tothe image capture apparatus which is attached on the column. The imagecapture apparatus may be moved up and/or down on the column as it isvertically mobile. The subject may move by himself and may move himselfthe image capture apparatus, directly or indirectly, for examplemanually or with a remote control or by giving instructions to anotherperson for moving it. Alternatively, the movements of the subject and/orthe image capture apparatus may be guided by another person such as theeye care professional.

Preferably, in step c), the inclination and/or position of the imagecapture apparatus is adjusted in order for the head of the subject to bein the field of the image capture apparatus.

Preferably, the image capture apparatus is positioned such that theimage capture apparatus optical axis is close or parallel to the gazedirection of the subject during the capture of said image of the head ofthe subject in step d).

In the case of the first embodiment, this may be achieved manually bythe subject.

Preferably, the image capture apparatus 12 is oriented such that itsoptical axis is parallel to the gaze axis GDL, GDR of the subject (FIGS.2 and 3).

When the image capture apparatus 12 is part of a smartphone or tablet,the optical axis of the image capture apparatus is usually perpendicularto the screen of the device. This screen is therefore placedperpendicularly to the gaze axis of the subject. This situation is shownon FIGS. 2 to 4.

This may be easily achieved in said particularly advantageousembodiment, where the portable electronic device 10 with the imagecapture apparatus 12 is pressed against the glass of the window 30. Thebody 11 of the portable electronic device 10 that supports the screen isthen applied against the glass of the window 30, meaning that theoptical axis OA of the image capture apparatus 12 is mostlyperpendicular to the glass of the window 30.

The subject may therefore easily look straight through the glass of thewindow 30, thereby having at least one of his gaze directions GDR, GDLperpendicular to the glass of the window 30 and parallel to the opticalaxis of the image capture apparatus 12.

In the situation of FIG. 2, where the entrance pupil P of the imagecapture apparatus 12 is aligned with the pupil PR of one of the eye ORof the subject, for example the right eye OR, and the target 20, theoptical axis of the image capture apparatus is superposed with the gazedirection GDR of this eye OR the subject.

In this case, an observation line OBLR1 linking the pupil PR of theright eye OR of the subject and the pupil P of the image captureapparatus 12 is superposed to the gaze direction GDR of this right eyeOR.

In the situation of FIG. 3, where the entrance pupil P of the imagecapture apparatus 12 is shifted relative to the gaze direction GDR ofthe subject, the optical axis OA of the image capture apparatus 12 isparallel to the gaze direction GDR of the subject.

In this case, an observation line OBLR2 linking the pupil of the righteye OR of the subject and the pupil P of the image capture apparatus 12forms a non zero angle with the gaze direction GDR of this right eye OR.

Alternatively, especially in the case where the subject holds the imagecapture apparatus without applying it against a window, the optical axisof the image capture apparatus 12 may be inclined compared to the gazeaxis GDR, GDL of the subject, as long as the eyes OL, OD of the subjectappear on the images captured, that is to say as long as the eyes OD, OLof the subject are in the field of the image capture apparatus 12.

This situation is represented with a portable electronic device 10A indashed lines on FIGS. 2 and 3.

In the second embodiment, the image capture apparatus may or may not beable to be inclined relative to the column. If it may be inclined, thisadjustment may be performed by the subject or by the operator. Otherwiseonly the position adjustment is achieved.

Alternatively, the pupil of the image capture apparatus may also beplaced between the eyes of the subject. It then remains close to both ofthe gaze directions of the subject.

In an embodiment, the image capture apparatus comprises an inertialmotion unit adapted to determine the angular position in space of thedevice, and a communication device adapted to send information on theangular position in space of the device to the subject and, in step c),the image capture apparatus provides information to the subject on theangular position of the device compared to a target angular position.

For example, the image capture apparatus provides information to thesubject on the angular position of the optical axis of the image captureapparatus compared to a horizontal axis or plane.

The information may be displayed on a screen of the electronic portabledevice or of the column. It may alternatively be given by a soundsignal.

This is especially the case when the image capture apparatus belongs toa portable electronic device such as a smartphone or a tablet.Smartphone and tablet may be equipped with gyroscopic means able todetermine their orientation in space. A target angular position may bespecified and calculation means of the portable electronic device may beprogrammed to achieve said comparison. The inertial motion unit may alsocomprise an accelerometer and/or a magnetometer.

Preferably, in step c), the gaze direction GDL of the other eye OL ofthe subject remains pointed to said visual target 20, as shown on FIG.4.

This means that the pupil P of the image capture apparatus 12 is placedclose or on the gaze direction GDR of one of the eye OR of the subject,while the other eye OL remains focused on the visual target 20.

To this end, the size of the electronic portable device 10 is limitedsuch that it does not obstruct the field of view of the other eye OL, ORof the subject. The other eye may therefore remain focused on the target20 (FIG. 4).

Alternatively, the image capture apparatus 12 may be shifted upward ordownward in order to allow the subject to keep both of his eyes OR, OLfocused on the target 20 (FIG. 3). When the image capture apparatus 12is shifted from the gaze directions GDR, GDL of the subject, such as inthe situation shown on FIG. 3, the subject may keep both of his eyesOL,OR focused on the visual target 20 while capturing the image in stepd).

Advantageously, accommodation of the eyes of the subject on the imagecapture apparatus is thus avoided.

This is particularly advantageous when the geometrico-morphologicalparameter is being determined in conditions of far vision.

Advantageously, in the case where the pupil of the image captureapparatus is placed between the eyes of the subject, the subject uses asmall portable electronic device that does not obstruct the vision ofthe subject when it is placed between the eyes of the subject. Thisallows him to keep both of his eyes focused on the visual target whilecapturing the image in step d). This small portable electronic device isfor example a smartphone and presents a typical width of about 5 to 8centimeters.

The entrance pupil of the image capture apparatus may then be at thesame level than the pupil of the eyes.

At step d), the image may be captured in natural posture, withoutaccommodation on the image capture apparatus 12.

In the case of the intermediate and near vision measurements,accommodation is expected. However, the use of the method allows keepingthe accommodation of the eye on a target placed at a predetermineddistance. The measurement corresponds then precisely to the visualconditions set by the visual target.

In any case, the fact that one of the eyes remains focused on the visualtarget leads to the capture of an image of the eyes in the visualconditions set by the visual target, with no perturbation due to theplacement of the image capture apparatus between the eyes and thetarget.

Alternatively, the gaze direction of both eyes of the subject may pointto said entrance pupil of the image-capture apparatus and the eyes maybe focused on this entrance pupil during said image capture in step d).This is taken into account in step e).

Step d)

In step d), an image of the head of the subject is captured by saidimage capture apparatus placed in the posture relative to the head ofthe subject determined in step c) of method according to the invention.

This image may be a two dimensional image or a three dimensional imageof the head of the subject.

In step d), the image capture is triggered by the subject orautomatically triggered by the image capture apparatus when the head ofthe subject is detected by said image capture apparatus.

In the first embodiment described here, the subject holds the portableelectronic device 10 in his hands and may directly manually trigger thecapture of the image when the image capture apparatus in positioned infront of his eyes as instructed, that is, with the pupil P of the imagecapture apparatus being on the gaze direction of one of his eyes orclose to the gaze direction of at least one of his eyes.

In the second embodiment described here, the image capture apparatus isplaced on a column. In this case, the subject preferably triggers thecapture of an image with a remote control. Alternatively, another personmay trigger the capture of the image, for example the eye careprofessional.

In all cases, the image capture apparatus may be programmed to recognizethe head of the subject in the field of the image capture apparatus andautomatically trigger the capture of the image when the head or moreprecisely, when the eyes of the subject is detected in said image. Theimage capture may also be triggered when an absence of movement isdetected, meaning that the image capture apparatus is correctlypositioned.

To this end, images are automatically captured and treated with asoftware or an application integrated in the image capture apparatus orthe portable electronic device or the column for recognizing the headand/or the eyes of the subject. The images may also be sent and treatedin another device or on a distant server comprising said software. Suchsoftware is well known from the man skilled in the art.

In step d), the subject may or may not wear the chosen frame in whichthe lens is to be fitted.

Advantageously, a reference element for scaling the image may be placedclose to the head of the subject and, in step d), an image of thisreference element may be captured with the image of the head of thesubject.

This reference element is preferably an object with specificinternational standard dimensions, such as a credit card. It mayalternatively be any object with a know dimension.

The subject may then determine this dimension and input this dimensionin the portable electronic device or in the column.

If the chosen frame is worn by the subject, the dimensions of the frame,usually indicated inside one of the branches of the frame, may be usedas a reference element for scaling the image.

Alternatively, no reference element is used and in step e), the imagemay be scaled using two reference point of the head of the subject, asdescribed later.

Step e)

In step e), the at least one geometrico-morphological parameter isdeduced from the image captured in step d).

More precisely, at least one of the following parameters is determined:interpupillary distance, half interpupillary distance, fitting heights.

In the case where, in step d), the gaze direction of both eyes of thesubject points to said pupil of the image-capture apparatus during thecapture of the image of the eyes of the subject, the distance betweenthe image capture apparatus and the eyes of the subject is taken intoaccount for determining said parameter.

In the first embodiment of the method, the portable electronic devicemay comprise GPS means and/or other positioning means allowingdetermining the position in space of the portable electronic device.

Different positioning means may be considered. For example, for a use inan eye care practitioner's office, a time-of-flight camera or a laserand a detection sensor may be added to the portable electronic device.At home, the individual may for example use a smartphone as the portableelectronic device and the inertial measurement unit of the smartphonecould be used as the positioning means.

This distance between the image capture apparatus and the eyes of thesubject is for example determined thanks to a calibration step.

In this case, in the calibration step, the subject places the portableelectronic device against his head, for example against his forehead,and records the position of his head thanks said GPS and/or positioningmeans. He then holds the device at the distance in which the image iscaptured and records this position as well. The distance between thehead of the subject and the image capture apparatus may then be easilydetermined. Alternatively, the distance between the head of the subjectand the image capture apparatus may be determined by other means, forexample by placing in the field of view of the image capture apparatus areference object with a know dimension such as a credit card or aprinted target for scaling the image.

In the cases where the pupil P of the image capture apparatus 12 is notplaced on the gaze direction of one of the eyes of the subject, an errorof parallax may be determined so that it may be taken into account fordetermining said parameter.

For example, when the pupil P of the image capture apparatus is placedbelow the gaze direction of the subject, an error of parallax may bedetermined in order to determine the fitting height of the subject.

When the pupil P of the image capture apparatus is shifted laterally,that is in a horizontal plane from the gaze direction of the subject, anerror of parallax may be determined in order to determine theinterpupillary or half interpupillary distances.

The interpupillary distance is determined by measuring the distancebetween the centers of the images of the pupils of said captured image.The right and left pupillary distances are determined by measuring thedistance between the centers of the images of each of the pupils and theimage of the middle of the bridge of the frame.

In an embodiment where the subject wears his real chosen frame duringstep d) of image capture, the fitting height may be determined bymeasuring the distance between the center of the image pupil of the eyeof the subject and the bottom edge of the image of the lens on saidimage captured.

It is deduced from this measure thanks to the scale factor of the imagedetermined and, optionally, after a correction due to a parallax error.

For example, for angle theta between the gaze direction GDR of thesubject and the observation line OBLR2 linking the pupil of the eye ORof the subject and the pupil P of the image capture apparatus 12, thecorrected value of the fitting height FH_(corrected) would be equal tothe initially determined fitting height FH_(measured) value based on theimage captured minus the product of the distance DVO between the eye andthe ophthalmic lens placed in the frame when worn by the subject (notshown on FIG. 3) and the tangent of the angle theta:FH_(corrected)=FH_(measured)−DVO.tan (theta).

The distance between the eye and the lens is determined as the distancebetween the center of rotation of the eye and the back surface of thelens. It is estimated to be about 24 millimeters.

The angle theta is determined for example thanks to the inertial motionunit and/or thanks to a treatment of the image captured. It may also beestimated. It is typically comprised between 1 and 10 degrees.

The angle theta may be defined in the application dedicated toimplementing the method according to the invention.

The individual or the eye care practitioner adjusts the position of thesmartphone with help from an indicator on a live video (for example inthe case of the eye care practitioner) or with help from a sonar signalfor the individual.

If no image of a reference element is present on the image captured toscale the image, the image may be scaled using two reference points ofthe head of the subject. For example, it is possible to detect thecenter of the image of the pupils of the subject on said captured imageand measure the interpupillary distance of the subject by another mean,for example with a pupilometer or a ruler. The image then can be scaledby using the value of the interpupillary distance thus determined andcomparing it to the distance between the images of the center of theimage of the pupils. Other remarkable points of the head may be used.

When the individual wears eyeglasses, the dimensions of the eyeglassesmay be used. It is for example possible to use the width of the right orleft circle or the width of the bridge, as noted inside one of thetemples.

In another embodiment, in step d), the subject wears no real frame. Inthis case, a three dimensional image of the head of the subject iscaptured by said image capture apparatus in step d).

A virtual representation of the frame chosen by the subject isdetermined in an additional step (block 600 of FIG. 1). Thisdetermination may comprise retrieving a model of said chosen frame froma database, scanning the real frame with a 3D scanner in order todetermine said virtual representation of the frame, or measuring some ofthe elements of the real frame (such as width, length of temples, bridgewidth . . . ).

Advantageously, when using the method according to the invention forordering eyeglasses online, a set of frames having geometric featuresadapted to the head of the subject is selected from a database of framesas a function of the three dimensional image of the head of the subjectcaptured. This database comprises the virtual representation ofdifferent frames.

The virtual representation of the chosen frame is called hereinafter thevirtual frame. It comprises at least a list of geometrical feature ofthe chosen frame, such as temple length, width of the bridge, width ofthe circles, wrap angle, total width.

The step of selecting the appropriate frame may be done by virtuallyfitted the virtual frame of the three dimensional image of the subjecthead, as is known for example from document W0201510173 8.

In a further step, the selected frames are submitted to the subject andthe subject chooses the frame he would like to purchase among thisselection.

In step e), said virtual frame is virtually fitted on the threedimensional image of the head of the subject and a two dimensional imageof the head of the subject wearing said virtual frame is deduced.

By virtually fitted, it is meant that the virtual frame is overlaid onthe three dimensional image of the head in order to be placed on thehead as it would be placed when worn by the subject. To this end,methods of virtual fitting are well known where remarkable part of thevirtual frame are superimposed on remarkable zones of the threedimensional image of the head.

Once the virtual frame is virtually fitted to the three dimensionalimage of the head of the subject, a projection of the three dimensionalrepresentation thus obtained is determined in a frontal plane. Thefrontal plane is perpendicular to the sagittal plane of the head of thesubject and to the Frankfurt plane of the head of the subject.

This projection forms a two dimensional image of the head equipped withthe virtual frame.

The fitting height of the subject equipped with the chosen frame isdetermined on the basis of the two dimensional image thus determined, asdescribed before. The right and left pupillary distances may also bedetermined based on the two dimensional image as the distance betweenthe center of the pupil of each eye and the middle of the bridge of theframe.

In the case where the subject is instructed to place the pupil of theimage capture apparatus on the gaze direction of one of his eyes, thatis, to superimpose the pupil of the image capture apparatus with thetarget, without specifying on the gaze direction of which eye it shouldbe placed, the dominant eye of the subject may also be determined as theeye corresponding to the gaze direction on which the subject places thepupil of the image capture apparatus. The image of the dominant eye isindeed positioned in the center of the captured image.

1. Method for determining at least one geometrico-morphologicalparameters of a subject in a natural posture for determining a visioncorrection equipment, wherein the following steps are performed: a) thesubject is placed (100) in a natural posture, in which at least one ofthe gaze directions (GDR, GDL) of the subject points to a visual target(20), b) an image capture apparatus (12) is placed (200) between thehead (50) of the subject and said visual target (20), c) the relativeposture of the image capture apparatus (12) and head (50) of the subjectis adjusted (300) in order for the pupil (P) of the image captureapparatus (12) to be positioned close to the gaze direction (GDR, GDL)of at least one of the eyes (OR, OL) of the subject, d) an image of thehead (50) of the subject is captured (400), e) the at least onegeometrico-morphological parameter is deduced (500) from this image. 2.The method for determining at least one geometrico-morphologicalparameters of a subject according to claim 1, wherein, in steps c) andd), the gaze direction (GDR, GDL) of at least one of the eyes (OR-, OL)of the subject points to said visual target (20).
 3. The method fordetermining at least one geometrico-morphological parameters of asubject according to claim 1, wherein: in step c), the relative postureof the image capture apparatus (12) and head (50) of the subject isadjusted by moving the image capture apparatus (12) without moving thehead (50) of the subject and, in step d), the gaze direction (GDR, GDL)of both eyes (OR, OL) of the subject points to said pupil (P) of theimage capture apparatus (12), in step e), the distance between the imagecapture apparatus (12) and the eyes (OR, OL) of the subject is takeninto account for determining said parameter.
 4. The method according toclaim 1, wherein, in step b), the image capture apparatus (12) belongsto a personal electronic portable device of the subject.
 5. The methodaccording to claim 1 4, wherein, in step a), the subject looks into thedistance through a window (30), in step b), the subject presses theimage capture apparatus (12) against the glass of the window (30) and instep c), the subject moves the image capture apparatus (12) against theglass of the window (30).
 6. The method according to claim 1, whereinthe steps a) to c) are performed by the subject himself: in step a), thesubject places himself in the natural posture and in step b) and c), theimage capture apparatus (12) is manually held and moved by the subject.7. The method according to claim 1, wherein the image capture apparatus(12) comprises an inertial motion unit adapted to determine the angularposition in space of the image capture apparatus (12), and acommunication device adapted to send information on the angular positionin space of the apparatus to the subject and, in step c), the imagecapture apparatus (12) provides information to the subject on theangular position of the apparatus compared to a target angular position.8. The method according to claim 1, wherein in step d), the imagecapture is triggered by the subject or automatically triggered by theimage capture apparatus (12) when the head (50) of the subject isdetected by said image capture apparatus (12).
 9. The method accordingto claim 1, 4, wherein the image capture apparatus is attached on acolumn and vertically mobile on this column.
 10. The method according toclaim 1, wherein, in step e), at least one of the following parametersis determined: interpupillary distance, half interpupillary distance,fitting heights.
 11. The method according to claim 1, wherein, in stepe) the dominant eye of the subject is also determined.
 12. The methodaccording to claim 1, wherein the image capture apparatus (12) ispositioned such that the image capture apparatus (12) optical axis (OA)is close or parallel to the gaze direction (GDR, GDL) of the subjectduring the capture of said image of the head (50) of the subject. 13.The method according to claim 1, wherein a reference element for scalingthe image is placed close to the head (50) of the subject and, in stepd), an image of the reference element is captured with the image of thehead (50) of the subject.
 14. The method according to claim 1, wherein,in step d), the subject wears no real frame and a three dimensionalimage of the head (50) of the subject is captured by said image captureapparatus (12), in step e), a virtual frame is virtually fitted on thethree dimensional image of the head (50) of the subject and a twodimensional image of the head (50) of the subject wearing said virtualframe is deduced, the fitting height parameter is determined on thebasis of this two dimensional image.
 15. System for determining at leastone geometrico-morphological parameters of a subject in a naturalposture for determining a vision correction equipment, comprising: avisual target (20) adapted to be placed in front of the subject, suchthat the subject is placed in a natural posture when at least one gazedirection (GDL, GDR) of the subject points to said visual target (20),an image capture apparatus (12) adapted to be placed between the head(50) of the subject and said visual target (20) and to capture an imageof the head (50) of the subject, adjusting means for adjusting theposition and/or orientation of the image capture apparatus (12) in orderfor the pupil (P) of the image capture apparatus (12) to be positionedclose to the gaze direction (GDR, GDL) of at least one of the eyes (OR,OL) of the subject, calculating means programmed for deducing the atleast one geometrico-morphological parameter from said image of the head(50) of the subject captured with said image capture apparatus (12). 16.The method for determining at least one geometrico-morphologicalparameters of a subject according to claim 2, wherein: in step c), therelative posture of the image capture apparatus (12) and head (50) ofthe subject is adjusted by moving the image capture apparatus (12)without moving the head (50) of the subject and, in step d), the gazedirection (GDR, GDL) of both eyes (OR, OL) of the subject points to saidpupil (P) of the image capture apparatus (12), in step e), the distancebetween the image capture apparatus (12) and the eyes (OR, OL) of thesubject is taken into account for determining said parameter.
 17. Themethod according to claim 2, wherein, in step b), the image captureapparatus (12) belongs to a personal electronic portable device of thesubject.
 18. The method according to claim 3, wherein, in step b), theimage capture apparatus (12) belongs to a personal electronic portabledevice of the subject.
 19. The method according to claim 2, wherein, instep a), the subject looks into the distance through a window (30), instep b), the subject presses the image capture apparatus (12) againstthe glass of the window (30) and in step c), the subject moves the imagecapture apparatus (12) against the glass of the window (30).
 20. Themethod according to claim 3, wherein, in step a), the subject looks intothe distance through a window (30), in step b), the subject presses theimage capture apparatus (12) against the glass of the window (30) and instep c), the subject moves the image capture apparatus (12) against theglass of the window (30).